1. Field of the Invention
The present invention relates to an apparatus and a method for attaching conductive metal balls to electrodes of a workpiece, and a method for forming bumps.
2. Description of the Prior Art
It is known to form bumps (protruding electrodes) on electrodes of a workpiece, such as a chip or a substrate, by attaching solder balls onto the electrodes of the workpiece, heating to melt the attached solder balls and then cooling the molten solder balls to solidify.
Further, it is known to use a pickup head for attaching the solder balls onto the electrodes of the workpiece as disclosed in U.S. Pat. No. 5,284,287. In this method, a large number of the solder balls are vacuum-absorbed to respective absorber holes formed at a bottom wall of the pickup head, and the pickup head is lowered and raised just above the workpiece so as to attach the solder balls onto the corresponding electrodes of the workpiece. According to this method, a large number of the solder balls can be attached onto the electrodes of the workpiece at a time.
As appreciated, when using the pickup head, it is essential that the solder balls are absorbed to all the absorber holes and that all the absorbed solder balls are attached onto the workpiece. Otherwise, the processed workpiece becomes defective. Accordingly, it is necessary to perform the solder ball attaching procedure while monitoring presence or absence of a solder ball pickup error or a solder ball attaching error. However, up to now, a system which can satisfy such a requirement has not yet been achieved.